Abstract
In this study, we employ a combination of various
in-situ
surface analysis techniques to investigate the thermally induced degradation processes in MAPbI
3
perovskite solar cells (PeSCs) as ...a function of temperature under air-free conditions (no moisture and oxygen). Through a comprehensive approach that combines
in-situ
grazing-incidence wide-angle X-ray diffraction (GIWAXD) and high-resolution X-ray photoelectron spectroscopy (HR-XPS) measurements, we confirm that the surface structure of MAPbI
3
perovskite film changes to an intermediate phase and decomposes to CH
3
I, NH
3
, and PbI
2
after both a short (20 min) exposure to heat stress at 100 °C and a long exposure (>1 hour) at 80 °C. Moreover, we observe clearly the changes in the orientation of CH
3
NH
3
+
organic cations with respect to the substrate in the intermediate phase, which might be linked directly to the thermal degradation processes in MAPbI
3
perovskites. These results provide important progress towards improved understanding of the thermal degradation mechanisms in perovskite materials and will facilitate improvements in the design and fabrication of perovskite solar cells with better thermal stability.
Abstract
Organic-inorganic hybrid perovskite solar cells (PSCs) have been extensively studied because of their outstanding performance: a power conversion efficiency exceeding 22% has been achieved. ...The most commonly used PSCs consist of CH
3
NH
3
PbI
3
(MAPbI
3
) with a hole-selective contact, such as 2,2′,7,7′-tetrakis(
N
,
N
-di-
p
-methoxyphenylamine)-9,9-spiro-bifluorene (spiro-OMeTAD), for collecting holes. From the perspective of long-term operation of solar cells, the cell performance and constituent layers (MAPbI
3
, spiro-OMeTAD, etc.) may be influenced by external conditions like temperature, light, etc. Herein, we report the effects of temperature on spiro-OMeTAD and the interface between MAPbI
3
and spiro-OMeTAD in a solar cell. It was confirmed that, at high temperatures (85 °C), I
−
and CH
3
NH
3
+
(MA
+
) diffused into the spiro-OMeTAD layer in the form of CH
3
NH
3
I (MAI). The diffused I
−
ions prevented oxidation of spiro-OMeTAD, thereby degrading the electrical properties of spiro-OMeTAD. Since ion diffusion can occur during outdoor operation, the structural design of PSCs must be considered to achieve long-term stability.
The effects of exchange current density, Tafel slope, system resistance, electrode area, light intensity, and solar cell efficiency were systematically decoupled at the converter-assisted ...photovoltaic–water electrolysis system. This allows key determinants of overall efficiency to be identified. On the basis of this model, 26.5% single-junction GaAs solar cell was combined with a membrane-electrode-assembled electrolysis cell (EC) using the dc/dc converting technology. As a result, we have achieved a solar-to-hydrogen conversion efficiency of 20.6% on a prototype scale and demonstrated light intensity tracking optimization to maintain high efficiency. We believe that this study will provide design principles for combining solar cells, ECs, and new catalysts and can be generalized to other solar conversion chemical devices while minimizing their power loss during the conversion of electrical energy into fuel.
Light trapping is a key issue in improving the efficiency of thin-film Si solar cells, and using a back reflector material plays a critical role in improving a cell's light-trapping efficiency. In ...this study, we developed n-type microcrystalline silicon oxide (n-μc-SiOx) films that are suitable for use as back reflectors in thin-film silicon solar cells. They exhibit a lower refractive index and lower absorption spectra, especially at long wavelengths of >700 nm, than conventional ZnO:Al materials, which are beneficial for this application. The n-μc-SiOx films were prepared by the PECVD (plasma-enhanced chemical vapor deposition) method and applied to the fabrication of back reflectors in μc-Si:H solar cells. We also characterized the changes in cell performance with respect to the refractive index, conductivity, and thickness of the n-μc-SiOx back reflectors. The novel back reflector boosts the total current density by up to 3.0% with the help of the enhanced long-wavelength response. It also improves open circuit voltage (Voc) and fill factor (FF), which may be attributed to the reduced shunt current caused by the anisotropic electrical characteristics of the n-μc-SiOx layer. Finally, we could achieve a conversion efficiency for the hydrogenated microcrystalline silicon (μc-Si:H) solar cells of up to 9.3% (Voc: 0.501 V, Jsc: 27.4 mA/cm2, FF: 0.68) using the n-μc-SiOx back reflector.
► We suggest new application of n-type microcrystalline silicon oxide (n-μc-SiOx). ► The n-μc-SiOx is applied as new back reflector material for thin-film Si solar cell. ► The n-μc-SiOx exhibits superior optical properties to conventional ZnO:Al. ► The new back reflector boosts not only the Jsc but also the Voc and the FF. ► The thickness of n-μc-SiOx back reflector is optimized for higher performance.
We observe >6% efficiency enhancement in silicon thin film solar cell using a p-type microcrystalline silicon oxide (μc-SiO:H) contact layer between transparent conducting oxide (TCO) electrode and ...the hydrogenated amorphous silicon (a-Si:H) layer. The role of the above contact layer is to reduce the Schottky barrier effect as well as the hetero-junction barrier formation at the interface. Despite its nanometer scale thickness, the properties of the contact layer significantly affect the solar parameters. Based on our results, p-type doped μc-SiO:H can be an ideal material as a contact layer due to its good optical response without noticeable degradation in its electrical property.
•We develop novel p-type contact layer for highly efficient a-Si triple junction cell.•We show that the role of the contact layer is to reduce the Schottkey barrier effect.•We develop the fabrication process for the novel p-mc-SiO contact layer.•We exhibit the efficiency enhancement in a cell using the novel contact layer.
Oxygen-controlled seed layer in Al-doped ZnO (ZnO:Al) thin films deposited by the industrially compatible dynamic dc magnetron sputter results in both enhanced electron mobilities and appropriate ...etched morphologies for the Si thin-film solar cells. At the relatively low deposition temperature of 300 °C, optimized ZnO:Al film grown on the seed layer has the carrier mobility of 45 cm 2 /V·s and proper postetching morphology with around 1-2-μm crater size. Reduced angular distribution of the (002) grains analyzed by the diffraction rocking curve is shown as the key structural feature for the improved carrier mobility. Finally, the performance of the microcrystalline Si solar cell on the developed ZnO:Al substrate shows high-efficiency potential of the tandem solar cell adapting this transparent conductive oxide substrate.
We have demonstrated subwavelength aluminum (Al) gratings with a period of 200
nm using nanoimprint lithography (NIL) and reactive ion etching (RIE). Al dry etching was attempted using the etch mask ...formed by NIL. The SiO
2 stamp with a size of 5
×
5
cm
2 was fabricated using laser interference lithography and RIE. The NIL process was optimized on Al/glass substrate and various imprint resists were tested for the Al etching. We could obtain a vertical etching profile and an etch selectivity of 2 with mrI-8020 imprint resist. The Al RIE combined with NIL will be useful for the realization of subwavelength Al gratings with a high aspect ratio.
We present the novel use of spectroscopic ellipsometry (SE) for the development of a-Si:H solar cell. SE is a very fast and useful tool to measure various optical properties of thin film. In the case ...of a-Si:H thin film analysis, generally, SE is used to estimate the film thickness, roughness, void fraction, optical constants such as (
n,
k), and so forth. In this study, optical parameters from SE measurements were analyzed with relation to structural and electrical properties of a-Si:H thin film for solar cell. By analyzing IR absorption spectra and conductivity measurements, it was affirmed that <
ε
2> and parameter
A by Tauc–Lorentz model fitting of SE data are representative parameters qualifying a-Si:H thin film, and that they have close relationships with FF and light induced degradation property of solar cells. Based on the analysis, solar cells that have i-layers with various
E
g
were optimized. By this research, easier and faster methodology to develop a-Si:H thin film for thin film Si solar cells using SE measurements was established.
Surface morphology and crystallinity of silicon p-layer have been investigated on the effect of various deposition conditions of RFPECVD in order to clarify crystalline nuclei evolution. ...Crystallinity increased with increasing hydrogen dilution, but decreased with increasing both RF input power and diborane doping. Microcrystalline nuclei size increased with increasing working pressure, RF input power and substrate temperature. However, surface morphology was not correlated with crystallinity or deposition rate. A film with relatively large nuclei but having rather low crystallinity can be prepared for some condition, and vice versa. In order to get a dense microcrystalline silicon intrinsic layer subsequently deposited, surface morphology control of microcrystalline p-layer seems to be important as well as crystallinity.
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